[reaction: see text] A new thioamide derivative of 8-hydroxyquinoline-benzothiazole was prepared, and its fluorogenic chemodosimetric behaviors toward transition-metal ions were investigated. The thioamide derivative showed highly Hg2+-selective fluorescence enhancing properties (167-fold) in 30% aqueous acetonitrile solution. The selective and sensitive signaling behaviors were found to originate from the Hg2+ ion induced transformation of the very weak fluorescent thioamide derivative into a highly fluorescent amide analogue.

A series of mono-, di-, and triphosphoniumsubstituted triarylboranes, [Mes 2 BAr P ]I ([2]I), [MesBAr P 2 ]I 2 ([3]I 2 ), and [BAr P 3 ]I 3 ([4]I 3 ) (Ar P = 4-(MePh 2 P)-2,6-Me 2 -C 6 H 2 ), were prepared from the corresponding neutral boranes 2a−4a. The crystal structure of [4]I 3 determined by X-ray diffraction study reveals peripheral decoration of aryl groups with phosphonium moieties. The anion affinity of the cationic boranes for fluoride and cyanide ions was investigated by UV−vis absorption titrations in aqueous solution. The triarylboranes, [2]I−[4]I 3 bind both fluoride and cyanide ions in a DMSO/H 2 O (7:3 v/v) mixture with high binding constants (K). Comparison of the K values of triarylboranes for fluoride reveals that fluorophilicity increases with the increasing number of phosphonium moieties: [2] + (K = 2.3 × 10 1 M −1 ) < [3] 2+ (3.6 × 10 5 M −1 ) < [4] 3+ (1.0 × 10 7 M −1 ). A similar trend is also observed in the cyanide binding, with K values that are greater by 2−4 orders of magnitude than those in the fluoride binding. These results indicate an apparent additive effect of multiple phosphonium substitutions on the Lewis acidity enhancement of triarylboranes. The triphosphonium borane [4]Cl 3 , a water-soluble form of [4]I 3 , was further utilized in evaluating the anion affinity in water. While [4] 3+ is shown to hardly bind fluoride in buffered water at pH 7, it binds cyanide with a high binding constant (1.7 × 10 7 M −1 ).

The o-carborane-triarylborane dyad shows high fluoride ion affinity through the trigonal-planar boron center while degradation to nido-carborane leads to a turn-on fluorescence response toward fluoride.

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